Implement a Simple Compass using SensorManager and SensorEventListener

Refer to the last exercise "Detect rotation around X, Y & Z axis, using SensorManager and SensorEventListener", Azimuth can be used to implement compass.



Create a custom view, MyCompassView, extends View. It display the drawing of our compass.
MyCompassView.java

package com.exercise.AndroidCompass;

import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.util.AttributeSet;
import android.view.View;

public class MyCompassView extends View {

private float direction = 0;
private Paint paint = new Paint(Paint.ANTI_ALIAS_FLAG);
private boolean firstDraw;

public MyCompassView(Context context) {
super(context);
// TODO Auto-generated constructor stub
init();
}

public MyCompassView(Context context, AttributeSet attrs) {
super(context, attrs);
// TODO Auto-generated constructor stub
init();
}

public MyCompassView(Context context, AttributeSet attrs, int defStyle) {
super(context, attrs, defStyle);
// TODO Auto-generated constructor stub
init();
}

private void init(){

paint.setStyle(Paint.Style.STROKE);
paint.setStrokeWidth(3);
paint.setColor(Color.WHITE);
paint.setTextSize(30);

firstDraw = true;
}

@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
// TODO Auto-generated method stub
setMeasuredDimension(MeasureSpec.getSize(widthMeasureSpec), MeasureSpec.getSize(heightMeasureSpec));
}

@Override
protected void onDraw(Canvas canvas) {
// TODO Auto-generated method stub

int cxCompass = getMeasuredWidth()/2;
int cyCompass = getMeasuredHeight()/2;
float radiusCompass;

if(cxCompass > cyCompass){
 radiusCompass = (float) (cyCompass * 0.9);
}
else{
 radiusCompass = (float) (cxCompass * 0.9);
}
canvas.drawCircle(cxCompass, cyCompass, radiusCompass, paint);
canvas.drawRect(0, 0, getMeasuredWidth(), getMeasuredHeight(), paint);

if(!firstDraw){

 canvas.drawLine(cxCompass, cyCompass,
   (float)(cxCompass + radiusCompass * Math.sin((double)(-direction) * 3.14/180)),
   (float)(cyCompass - radiusCompass * Math.cos((double)(-direction) * 3.14/180)),
   paint);

 canvas.drawText(String.valueOf(direction), cxCompass, cyCompass, paint);
}

}

public void updateDirection(float dir)
{
firstDraw = false;
direction = dir;
invalidate();
}

}

Modify the layout file, main.xml, to add MyCompassView.

 android:orientation="vertical"
 android:layout_width="fill_parent"
 android:layout_height="fill_parent"
 >
 android:layout_width="fill_parent"
 android:layout_height="wrap_content"
 android:text="@string/hello"
 />
class="com.exercise.AndroidCompass.MyCompassView"
android:id="@+id/mycompassview"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
/>

Modify the main code, AndroidCompass.java, to handle SensorManager and SensorEventListener.

package com.exercise.AndroidCompass;

import java.util.List;

import android.app.Activity;
import android.content.Context;
import android.hardware.Sensor;
import android.hardware.SensorEvent;
import android.hardware.SensorEventListener;
import android.hardware.SensorManager;
import android.os.Bundle;
import android.widget.Toast;

public class AndroidCompass extends Activity {

private static SensorManager mySensorManager;
private boolean sersorrunning;
private MyCompassView myCompassView;

 /** Called when the activity is first created. */
 @Override
 public void onCreate(Bundle savedInstanceState) {
     super.onCreate(savedInstanceState);
     setContentView(R.layout.main);
  
     myCompassView = (MyCompassView)findViewById(R.id.mycompassview);
  
     mySensorManager = (SensorManager)getSystemService(Context.SENSOR_SERVICE);
     List mySensors = mySensorManager.getSensorList(Sensor.TYPE_ORIENTATION);
  
     if(mySensors.size() > 0){
      mySensorManager.registerListener(mySensorEventListener, mySensors.get(0), SensorManager.SENSOR_DELAY_NORMAL);
      sersorrunning = true;
      Toast.makeText(this, "Start ORIENTATION Sensor", Toast.LENGTH_LONG).show();
    
     }
     else{
      Toast.makeText(this, "No ORIENTATION Sensor", Toast.LENGTH_LONG).show();
      sersorrunning = false;
      finish();
     }
 }

 private SensorEventListener mySensorEventListener = new SensorEventListener(){

@Override
public void onAccuracyChanged(Sensor sensor, int accuracy) {
 // TODO Auto-generated method stub

}

@Override
public void onSensorChanged(SensorEvent event) {
 // TODO Auto-generated method stub
 myCompassView.updateDirection((float)event.values[0]);
}
 };

@Override
protected void onDestroy() {
// TODO Auto-generated method stub
super.onDestroy();

if(sersorrunning){
 mySensorManager.unregisterListener(mySensorEventListener);
}
}

}

Modify AndroidManifest.xml to disable the auto-rotate feature, otherwise it will point to wrong direction.

Download the files.

Related Article:
Implement a Simple Horizontal Indicator using SensorManager and SensorEventListener